Organisms exchange substances with their environment (AQA AS Biology) PART 4 of 5 TOPICS

TOPICS: Surface area to volume ratio  Gas exchange  Digestion and absorption  Mass transport in animals  Mass transport in plants

Mass transport in animals – Heart disease:

Coronary heart disease is where the arteries supplying the heart with oxygenated blood and nutrients (coronary arteries) are narrowed causing the blood supply to reduce. This means that the heart has to work harder to force blood through the narrowed vessels therefore blood pressure increases. The outcomes can be any of these:

• Angina: This is chest pain due to severe shortage of blood to the heart muscle – cells do not die. The pain only occurs when the person is active and not at rest.
• Heart attack (myocardial infarction): This is when a coronary artery is completely blocked by a thrombus (dried red blood cells). This causes the blood supply to reduce majorly leading to heart muscle cells dying which is fatal.
• Heart failure: Some blockages are not as fatal as the thrombus that leads to heart attacks. Instead they will lead to weakening of the muscle which means the heart will be less efficient for pumping. Often there is an accumulation of blood on the right side of the heart creating an enlargement.

The main cause of coronary heart disease are:

• Atherosclerosis: This is where fatty deposits of cholesterol and plaques of white blood cells block the artery. This deposit may even cause a rupture in the artery walls creating a thrombus which can break and block arteries in the heart as well as the brain.
• Aneurysm: This is where the artery walls weaken causing it to collapse. This means that the blood pressure is not maintained throughout the artery. Sometimes the weakened walls can burst as a higher pressure is needed to move the blood leading to severe loss of blood (haemorrhage). This process which can occur in the brain is more commonly known as stroke.

Smoking is one of the top causes of heart disease.